In a communications system, such as a cellular radio system using TDMA for communications on the so-called reverse or upstream channel from a terminal to a base station, it is known that the SINR of a received signal can be used as a signal quality parameter for various procedures such as hand-off, adaptive channel allocation, dynamic power control, and cell tiering.
The channel characteristics fluctuate with time and the received signals are subject to fading, so that averaging over a number of time slots of the channel is necessary to obtain a sufficiently accurate determination (measurement or estimation) of the SINR. The number of time slots over which averaging is necessary depends on the manner in which the SINR is determined, but in any event increases with slower channel fluctuations, and hence with slower speeds of a mobile terminal. To be of practical use, typically SINR estimates accurate to within 1 dB of the average SINR may be required within 2 seconds, during which there may be 100 time slots of the channel.
In view of these factors, practical determination of SINR in real time for use as a signal quality parameter has not readily been achieved. Consequently, the procedures mentioned above have commonly used the received signal strength indicator (RSSI) as a signal quality parameter instead of the SINR, but this is undesirable because the RSSI does not reliably represent the signal quality. For example, the RSSI may be large due to co-channel interference, when the actual signal quality and SINR are small.
An object of this invention, therefore, is to provide an improved method of and apparatus for determining SINR.